spatial network method

Hi everybody,
I am working on a PIFA antenna, and I am in the phase of theorical studying, I found in some thesis that this kind of antenna were studied by using a method called "spatial network method", but the matter is that I have two thesis and each one give a version the first told that the author who study it is with the SNM is : "Hirasawa" and the second told that it is "Yoshida".
So if any one have some papers about it they be welcome .
thanks in advance.
best regards